1. Technical Field
The present invention generally relates to evaporative emission control systems for automotive vehicles and, more particularly, to a leak detection assembly and a method of determining if a leak is present in an evaporative emission control system of an automotive vehicle.
2. Discussion
Modern gasoline powered automotive vehicles typically include a fuel tank and an evaporative emission control system that collects fuel vapors generated in the fuel tank. The evaporative emission control system includes a vapor collection canister, usually containing activated carbon, to collect and store fuel vapors. The canister collects fuel vapors which are displaced from the fuel tank during refueling of the automotive vehicle or from increases in fuel temperature.
The evaporative emission control system also includes a purge valve between the intake manifold of the engine and the canister. When conditions are conducive to purging, a controller opens the purge valve a predetermined amount to purge the canister. That is, the collected fuel vapors are drawn into the intake manifold from the canister for ultimate combustion within the engine.
It has recently become desirable to check evaporative emission control systems for leaks. To this end, on board vehicle diagnostic systems have been developed to determine if a leak is present in a portion of the evaporative emission control system. One such diagnostic method utilizes negative pressurization to check for leaks. In this method, a vent valve is used to seal the canister vent, a sensor to monitor system pressure, and a purge valve to draw a vacuum on the evaporative emission control system. As the vacuum is drawn, the method monitors whether a loss of vacuum occurs within a specified period of time. If so, a leak is presumed to be present.
Diagnostic systems also exist for determining the presence of a leak in an evaporative emission control system which utilize positive pressurization rather than negative pressurization. In positive pressurization systems, the evaporative emission control system is pressurized to a set pressure, typically through use of an air pump. Thereafter, a sensor detects whether a loss of pressure occurs over a certain amount of time.
While positive and negative pressurization systems are useful, there is room for improvement in the art. For instance, it would be desirable to provide a leak detection system which does not require either positive or negative pressurization of the system from an outside source. Additionally, it would be desirable to provide a leak detection system which functions when the vehicle is not operating. This would eliminate many of the complicated issues which make leak detection on an operating vehicle very difficult.
It is one object of the present invention to provide a leak detection assembly for use in testing the integrity of an evaporative emission control system for an automotive vehicle.
It is another object of the present invention to provide a leak detection method having a device for sealing the evaporative emission control system such that an internal pressure thereof is isolated from external influences.
It is yet another object of the present invention to provide a leak detection method having a device for monitoring the internal pressure of the evaporative emission control system after it has been sealed such that very small, moderate, and large leaks may be separately detected by noting if the pressure within the sealed evaporative emission control system goes below atmospheric pressure over predetermined periods of time as the evaporative emission control system components cool.
It is still yet another object of the present invention to provide a leak detection method for testing the rationality of the device used for monitoring the internal pressure of the evaporative emission control system.
It is another object of the present invention to provide a leak detection method for periodically cleaning the device for sealing the evaporative emission control system.
Some of the above and other objects are provided by a method of detecting a small or gross leak in an evaporative emission control system of an automotive vehicle. The method includes initially purging and then sealing the evaporative emission control system. A vacuum switch coupled to the evaporative emission control system is then monitored for an opening event caused by a loss of a vacuum created in the evaporative emission control system. If said opening event is detected, the method determines if a leak check timer has exceeded a first or second predetermined threshold value. If the leak check timer has not exceeded said first predetermined threshold value a first fault code is set indicating that a gross leak has been detected. If the leak check timer has not exceeded the second predetermined threshold value, a second fault code is set indicating that a small leak has been detected. The first threshold value corresponds to an amount of time required for a leak to be detected having a diameter of about 0.070 inches or greater. The second threshold value corresponds to an amount of time required for a leak to be detected having a diameter of about 0.040 inches or greater.